The present invention relates to soap formulations which do not form a scum in hard water.
The oldest, best known, or by far the most important surface active agents are soaps. The salient disadvantage of the soaps is their instability toward heavy-metal ions, particularly the calcium and magnesium ions found in hard water, as the calcium and magnesium salts of the fatty acids are quite insoluble in water. Soap, however, has at least two major points of superiority, i.e., low cost and high detergent powers in most of the cleaning operations encountered practically.
Fatty acid soaps in moderately hard water are known to provide excellent soil removal and very good suspension of soil in the wash cycle of laundering if sufficient quantities of soap are used. However, in the subsequent step of rinsing, a smaller amount of residual soap, which cannot be totally extracted from the laundry items, comes into contact with a relatively large amount of hard water cations. This rinsing step can reprecipitate lime soap, carrying with it small but ultimately visible amounts of insoluble dirt and other "color bodies".
Thus, in hard water, soap is less economical to use than detergents because a much higher concentration of soap is required to titrate the hardness. Soap is also poorly soluble in cool water, making it undesirable for use in washing many delicate synthetic fabrics as well as some colored fabrics, the colors of which may bleed in hot water.